The present invention relates in general to a scroll type compressor (hereinafter referred to as "scroll compressor" for clarification and simplification only) and more particularly to a driving mechanism comprising primarily a crank shaft and an eccentric bushing wherein the scroll driving mechanism is responding to variance of radius of orbiting motion of movable scroll part or member in the scroll compressor. Further, the present invention relates to a compression mechanism including a vacuum pump and an expansion device which employs the similar mechanism as the scroll compressor employing a movable scroll member.
A scroll compressor including a movable scroll member which has a variable orbit radius, whose detailed structure and operation will be described presently, generally has a unitary structure of a counter weight and an eccentric bush is supported by a crank pin fixed to a large-diameter portion of a main axis of the crank shaft in such a manner that the center of gravity is spaced or shifted from the fulcrum (supporting point). When an orbiting speed is increased, the counter weight is inclined, by its centrifugal force, toward the main axis of the crank shaft.
The inclination of the counter weight as described above will possibly provide an unexpected contact with peripheral parts and elements, with the result of damages in the peripheral parts and elements in the worst case.
An attempt was made to solve the problems and disadvantages described above in the scroll compressor employing a slide type variable orbiting radius mechanism as disclosed in Japanese Utility Model Publication (Unexamined) 4-87382 (1992). For the purpose of clarification and simplification, the disclosure of the Japanese U.M. Publication will now be explained.
Referring to FIGS. 1 and 2, a movable scroll member rotatably holds an eccentric bush 3 through a radial needle bearing 22. The eccentric bush 3 is unitarily formed with a counter weight 2 and snugly adapted to a crank pin 110. The eccentric bush 3 has a bush hole 30 into which the crank pin 110 is fitted. The crank pin 110 is eccentrically connected to the large diameter portion 10 of a main shaft or a crank shaft 1. A groove or a hole is formed to extend in a radial direction of the crank pin 110. The groove has a size which is larger than that of the crank pin 110. So that, the eccentric bush 3 can slide therealong in the radial direction of the crank pin 110. In other words, the groove permits to vary the orbiting radius. If the crank pin 110 is closely fitted in the bush hole 30, it is not likely that the counter weight 2 is inclined by a centrifugal force added to the counter weight. However, there is a gap or a "play" of the groove and, accordingly, the counter weight is inclined when a centrifugal force is added by the reasons set forth below.
In the scroll compressor of the structure as described above, the eccentric bush 3 is supported by a single crank pin. In addition, the counter weight 2 is fitted to the eccentric bush 3. Thus, the center of gravity of the unitary structure of the counter weight 2 and the eccentric bush 3 is eccentrically located or offset towards the counter weight 2.
In general, balancing is made by the use of the crank pin 110. When a centrifugal force is added, the balanced condition is broken, with the result of inclination of the counter weight 2. This is the reason why the counter weight is inclined. This inclination is controlled by an inclination controller 24. A bolt may be used for the inclination controller 24.
The conventional scroll compressor of a variable orbit-radius type has a serious problem of inclination of the counter weight as described above and this problem of the counter weight inclination possibly results in damages of the peripheral parts and elements due to the unexpected contact of the counter weight against the peripheral parts and elements.
In addition to the above, a slide groove of a substantially oblong shape serves to permit the variable orbit radius and, therefore, the shapes of the crank pin of the large diameter portion of the main axis and the hole of the crank pin of the eccentric bush are special and unusual and, therefore, requires substantial working costs.
The problem of counter weight inclination is supposed to be satisfactorily solved by the attempt of using a inclination restriction bolt as disclosed in aforementioned Japanese Utility Model Publication (Unexamined) 4-87382. However, the formation of the slide groove needs a special working and technique, resulting in an increase of production costs and this cost problem has not yet been solved.
Further, additional mechanism of applying the inclination restriction bolt must be provided which results in a further increase of working and production costs.